The objective of this project is to develop a dedicated clinical system for testing and analyzing ocular motility. Commercially, our goal is to produce a low-cost, user-friendly hardware/software package utilizing the latest micro-processor and memory technology specifically designed to allow clinical personnel with no computer training to quantitatively analyze (on-line) the eye movements produced in patients during pursuit tracking, random saccade tests, caloric irrigation, optokinetic and positional nystagmus testing and rotatory tests of vestibular function. Innovative features of the system will include a new (proprietary) technique for measuring eye movements based electrical impedance phase angle shifts and a programmable solid-state stimulator for smooth-pursuit, random saccade and optokinetic testing. Phase I of the project is dedicated to developing a new thermal probe for caloric stimulation of the labyrinth during clinical evaluation of vestibulo-ocular reflex function. The caloric probe stimulator will be a compact, battery-powered portable instrument utilizing a solid-state thermoelectric heat pump arranged in a feedback servo-loop under control of a microprocessor which can be programmed to deliver calibrated thermal stimuli of known caloric content at temperatures from 5 to 50 degrees C. These features, which are presently unavailable on any other instrument, afford new opportunities for improving the reliability and clinical significance of the caloric test.